Method and apparatus for scene detection based encoding

ABSTRACT

In a method, whether a sequence of pictures includes a flash picture is determined. The flash picture is associated with a scene change between (i) a first scene of a picture of the sequence of pictures and (ii) a second scene of a prior picture and a subsequent picture of the picture in the sequence of pictures. The scene change is determined based on a content change between the first scene and the second scene being larger than a threshold. An encoding process is performed on a current picture in the sequence of pictures in response to (i) the picture being determined as the flash picture and (ii) the picture being the current picture.

INCORPORATION BY REFERENCE

The present application claims the benefit of priority to U.S.Provisional Application No. 63/287,445, “Method and Apparatus for SceneDetection Based Encoding” filed on Dec. 8, 2021, which is incorporatedby reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Uncompressed digital images and/or video can include a series ofpictures, each picture having a spatial dimension of, for example,1920×1080 luminance samples and associated chrominance samples. Theseries of pictures can have a fixed or variable picture rate (informallyalso known as frame rate), of, for example 60 pictures per second or 60Hz. Uncompressed image and/or video has specific bitrate requirements.For example, 1080p60 4:2:0 video at 8 bit per sample (1920×1080luminance sample resolution at 60 Hz frame rate) requires close to 1.5Gbit/s bandwidth. An hour of such video requires more than 600 GBytes ofstorage space.

One purpose of image and/or video coding and decoding can be thereduction of redundancy in the input image and/or video signal, throughcompression. Compression can help reduce the aforementioned bandwidthand/or storage space requirements, in some cases by two orders ofmagnitude or more. Although the descriptions herein use videoencoding/decoding as illustrative examples, the same techniques can beapplied to image encoding/decoding in similar fashion without departingfrom the spirit of the present disclosure. Both lossless compression andlossy compression, as well as a combination thereof can be employed.Lossless compression refers to techniques where an exact copy of theoriginal signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transformprocessing, quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding used in, for example, MPEG-2 generation codingtechnologies, does not use intra prediction. However, some newer videocompression technologies include techniques that attempt to performprediction based on, for example, surrounding sample data and/ormetadata obtained during the encoding and/or decoding of blocks of data.Such techniques are henceforth called “intra prediction” techniques.Note that in at least some cases, intra prediction is using referencedata only from the current picture under reconstruction and not fromreference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology, aspecific technique in use can be coded as a specific intra predictionmode that uses the specific technique. In certain cases, intraprediction modes can have submodes and/or parameters, where the submodesand/or parameters can be coded individually or included in a modecodeword, which defines the prediction mode being used. Which codewordto use for a given mode, submode, and/or parameter combination can havean impact in the coding efficiency gain through intra prediction, and socan the entropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesof already available samples. Sample values of neighboring samples arecopied into the predictor block according to a direction. A reference tothe direction in use can be coded in the bitstream or may itself bepredicted.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from the 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes) defined inH.265. The point where the arrows converge (101) represents the samplebeing predicted. The arrows represent the direction from which thesample is being predicted. For example, arrow (102) indicates thatsample (101) is predicted from a sample or samples to the upper right,at a 45 degree angle from the horizontal. Similarly, arrow (103)indicates that sample (101) is predicted from a sample or samples to thelower left of sample (101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore, no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples indicated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from samplesto the upper right, at a 45 degree angle from the horizontal. In thatcase, samples S41, S32, S23, and S14 are predicted from the samereference sample R05. Sample S44 is then predicted from reference sampleR08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013).Currently, JEM/VVC/BMS can support up to 65 directions. Experiments havebeen conducted to identify the most likely directions, and certaintechniques in the entropy coding are used to represent those likelydirections in a small number of bits, accepting a certain penalty forless likely directions. Further, the directions themselves can sometimesbe predicted from neighboring directions used in neighboring, alreadydecoded, blocks.

FIG. 1B shows a schematic (110) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction direction bits that represent thedirection in the coded video bitstream can be different from videocoding technology to video coding technology. Such mapping can range,for example, from simple direct mappings, to codewords, to complexadaptive schemes involving most probable modes, and similar techniques.In most cases, however, there can be certain directions that arestatistically less likely to occur in video content than certain otherdirections. As the goal of video compression is the reduction ofredundancy, those less likely directions will, in a well working videocoding technology, be represented by a larger number of bits than morelikely directions.

Image and/or video coding and decoding can be performed usinginter-picture prediction with motion compensation. Motion compensationcan be a lossy compression technique and can relate to techniques wherea block of sample data from a previously reconstructed picture or partthereof (reference picture), after being spatially shifted in adirection indicated by a motion vector (MV henceforth), is used for theprediction of a newly reconstructed picture or picture part. In somecases, the reference picture can be the same as the picture currentlyunder reconstruction. MVs can have two dimensions X and Y, or threedimensions, the third being an indication of the reference picture inuse (the latter, indirectly, can be a time dimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described with reference toFIG. 2 is a technique henceforth referred to as “spatial merge”.

Referring to FIG. 2 , a current block (201) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (202 through 206, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video and/ordecoding includes processing circuitry.

According to an aspect of the disclosure, a method of video encodingperformed in a video encoder is provided. In the method, whether asequence of pictures includes a flash picture can be determined. Theflash picture can be associated with a scene change between (i) a firstscene of a picture of the sequence of pictures and (ii) a second sceneof a prior picture and a subsequent picture of the picture in thesequence of pictures. The scene change can be determined based on acontent change between the first scene and the second scene being largerthan a threshold. An encoding process can be performed on a currentpicture in the sequence of pictures in response to (i) the picture beingdetermined as the flash picture and (ii) the picture being the currentpicture.

In an example, the picture can be determined as the flash picture basedon a contrast difference between the first scene and the second scenebeing larger than the threshold. In an example, the picture can bedetermined as the flash picture based on a feature difference betweenthe first scene and the second scene being larger than the threshold.

When the encoding process includes the temporal filter process, thetemporal filter process may not be performed on the picture based on thepicture being determined as the flash picture and being the currentpicture.

When the encoding process includes a temporal filter process, thepicture can be excluded as a reference picture in the temporal filterprocess based on the picture being determined as the flash picture andnot being the current picture.

In response to the picture being excluded as the reference picture inthe temporal filter process, another picture can be added to thesequence of pictures as a reference picture for the temporal filterprocess. Thus, a total number of reference pictures for the temporalfilter process can remain constant. The other picture and the picturecan be positioned at a same temporal side of the current picture in thetemporal filter process.

The encoding process can include one of an attribute adjustment, a costestimation, or a luma mapping with chroma scaling (LMCS) process. TheLMCS process can include in-loop mapping of a luma component of thecurrent picture and a scaling of a luma-dependent chroma residual of thecurrent picture.

When the encoding process includes the attribute adjustment, the picturecan be moved to a higher temporal level in the sequence of picturesbased on the picture being the flash picture.

When the encoding process includes the attribute adjustment, a slicetype of the picture can be set as a P slice based on the picture beingthe flash picture.

When the encoding process includes the attribute adjustment, the picturecan be determined as a non-reference picture of the current picturebased on the picture being the flash picture and not being the currentpicture.

When the encoding process includes the cost estimation, the costestimation can be performed to generate a difference between the currentpicture and a prediction that is based on a weighted combination of thepicture and another reference picture of the current picture based onthe picture being determined as the flash picture and not being thecurrent picture.

In some embodiments, at least one of bi-direction optical flow (BDOF) ordecoder side motion vector refinement (DMVR) can be disabled for thecurrent picture in the encoding process in response to (i) the picturebeing determined as the flash picture and being a reference picture ofthe current picture, and (ii) the current picture being a B type picturewith two reference picture lists.

When the encoding process includes the LMCS process, the LMCS processcan be disabled for the picture based on the picture being determined asthe flash picture.

When the encoding process includes the LMCS process, based on thepicture being determined as the flash picture, a set of LMCS parameterscan be determined for the picture based on an LMCS picture analysis. TheLMCS can be performed on the picture based on the determined set of LMCSparameters.

When the encoding process includes the LMCS process, the LMCS can beperformed on the picture based on a predefined set of LMCS parameters inresponse to the picture being determined as the flash picture. Thepredefined set of LMCS parameters can be generated by training aplurality of general flash pictures.

According to another aspect of the disclosure, an apparatus is provided.The apparatus includes processing circuitry. The processing circuitrycan be configured to perform any of the methods for videoencoding/decoding.

Aspects of the disclosure also provide a non-transitorycomputer-readable storage medium storing instructions which whenexecuted by a computer for video encoding and/or decoding cause thecomputer to perform any of the methods for video encoding/decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes.

FIG. 1B is an illustration of exemplary intra prediction directions.

FIG. 2 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 6 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 7 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 8 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 9 shows a schematic illustration of an exemplary extended codingunit (CU) region for bi-directional optical flow (BDOF).

FIG. 10 shows a schematic illustration of an example of decoding sidemotion vector refinement.

FIG. 11 shows a schematic illustration of an example of flash picturedetection.

FIG. 12 shows a schematic illustration of an exemplary noise detectionprocess.

FIG. 13 shows a schematic illustration of an exemplary luma mapping withchroma scaling architecture.

FIG. 14 shows a schematic illustration of an exemplary flash picture intemporal filtering references.

FIG. 15 shows a flow chart outlining an exemplary encoding processaccording to some embodiments of the disclosure.

FIG. 16 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 3 illustrates an exemplary block diagram of a communication system(300). The communication system (300) includes a plurality of terminaldevices that can communicate with each other, via, for example, anetwork (350). For example, the communication system (300) includes afirst pair of terminal devices (310) and (320) interconnected via thenetwork (350). In the FIG. 3 example, the first pair of terminal devices(310) and (320) performs unidirectional transmission of data. Forexample, the terminal device (310) may code video data (e.g., a streamof video pictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that perform bidirectionaltransmission of coded video data, for example, during videoconferencing.For bidirectional transmission of data, in an example, each terminaldevice of the terminal devices (330) and (340) may code video data(e.g., a stream of video pictures that are captured by the terminaldevice) for transmission to the other terminal device of the terminaldevices (330) and (340) via the network (350). Each terminal device ofthe terminal devices (330) and (340) also may receive the coded videodata transmitted by the other terminal device of the terminal devices(330) and (340), and may decode the coded video data to recover thevideo pictures and may display video pictures at an accessible displaydevice according to the recovered video data.

In the example of FIG. 3 , the terminal devices (310), (320), (330) and(340) are respectively illustrated as servers, personal computers andsmart phones but the principles of the present disclosure may be not solimited. Embodiments of the present disclosure find application withlaptop computers, tablet computers, media players, and/or dedicatedvideo conferencing equipment. The network (350) represents any number ofnetworks that convey coded video data among the terminal devices (310),(320), (330) and (340), including for example wireline (wired) and/orwireless communication networks. The communication network (350) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(350) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 4 illustrates, as an example of an application for the disclosedsubject matter, a video encoder and a video decoder in a streamingenvironment. The disclosed subject matter can be equally applicable toother video enabled applications, including, for example, videoconferencing, digital TV, streaming services, storing of compressedvideo on digital media including CD, DVD, memory stick and the like, andso on.

A streaming system may include a capture subsystem (413), that caninclude a video source (401), for example a digital camera, creating forexample a stream of video pictures (402) that are uncompressed. In anexample, the stream of video pictures (402) includes samples that aretaken by the digital camera. The stream of video pictures (402),depicted as a bold line to emphasize a high data volume when compared toencoded video data (404) (or coded video bitstreams), can be processedby an electronic device (420) that includes a video encoder (403)coupled to the video source (401). The video encoder (403) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (404) (or encoded video bitstream),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (402), can be stored on a streamingserver (405) for future use. One or more streaming client subsystems,such as client subsystems (406) and (408) in FIG. 4 can access thestreaming server (405) to retrieve copies (407) and (409) of the encodedvideo data (404). A client subsystem (406) can include a video decoder(410), for example, in an electronic device (430). The video decoder(410) decodes the incoming copy (407) of the encoded video data andcreates an outgoing stream of video pictures (411) that can be renderedon a display (412) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (404),(407), and (409) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows an exemplary block diagram of a video decoder (510). Thevideo decoder (510) can be included in an electronic device (530). Theelectronic device (530) can include a receiver (531) (e.g., receivingcircuitry). The video decoder (510) can be used in the place of thevideo decoder (410) in the FIG. 4 example.

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510). In an embodiment, one coded videosequence is received at a time, where the decoding of each coded videosequence is independent from the decoding of other coded videosequences. The coded video sequence may be received from a channel(501), which may be a hardware/software link to a storage device whichstores the encoded video data. The receiver (531) may receive theencoded video data with other data, for example, coded audio data and/orancillary data streams, that may be forwarded to their respective usingentities (not depicted). The receiver (531) may separate the coded videosequence from the other data. To combat network jitter, a buffer memory(515) may be coupled in between the receiver (531) and an entropydecoder/parser (520) (“parser (520)” henceforth). In certainapplications, the buffer memory (515) is part of the video decoder(510). In others, it can be outside of the video decoder (510) (notdepicted). In still others, there can be a buffer memory (not depicted)outside of the video decoder (510), for example to combat networkjitter, and in addition another buffer memory (515) inside the videodecoder (510), for example to handle playout timing. When the receiver(531) is receiving data from a store/forward device of sufficientbandwidth and controllability, or from an isosynchronous network, thebuffer memory (515) may not be needed, or can be small. For use on besteffort packet networks such as the Internet, the buffer memory (515) maybe required, can be comparatively large and can be advantageously ofadaptive size, and may at least partially be implemented in an operatingsystem or similar elements (not depicted) outside of the video decoder(510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such as arender device (512) (e.g., a display screen) that is not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as shown in FIG. 5 . The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI) messages or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (520) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (520) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (520) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (515), so as tocreate symbols (521).

Reconstruction of the symbols (521) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by subgroup controlinformation parsed from the coded video sequence by the parser (520).The flow of such subgroup control information between the parser (520)and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values, thatcan be input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform unit(551) can pertain to an intra coded block. The intra coded block is ablock that is not using predictive information from previouslyreconstructed pictures, but can use predictive information frompreviously reconstructed parts of the current picture. Such predictiveinformation can be provided by an intra picture prediction unit (552).In some cases, the intra picture prediction unit (552) generates a blockof the same size and shape of the block under reconstruction, usingsurrounding already reconstructed information fetched from the currentpicture buffer (558). The current picture buffer (558) buffers, forexample, partly reconstructed current picture and/or fully reconstructedcurrent picture. The aggregator (555), in some cases, adds, on a persample basis, the prediction information the intra prediction unit (552)has generated to the output sample information as provided by thescaler/inverse transform unit (551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensated,block. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (521) pertaining to the block, these samples can beadded by the aggregator (555) to the output of the scaler/inversetransform unit (551) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (557) from where themotion compensation prediction unit (553) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (553) in the form of symbols (521) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (557) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520). Videocompression can also be responsive to meta-information obtained duringthe decoding of previous (in decoding order) parts of the coded pictureor coded video sequence, as well as responsive to previouslyreconstructed and loop-filtered sample values.

The output of the loop filter unit (556) can be a sample stream that canbe output to the render device (512) as well as stored in the referencepicture memory (557) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (520)), the current picture buffer (558) can becomea part of the reference picture memory (557), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology or a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (531) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (510) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows an exemplary block diagram of a video encoder (603). Thevideo encoder (603) is included in an electronic device (620). Theelectronic device (620) includes a transmitter (640) (e.g., transmittingcircuitry). The video encoder (603) can be used in the place of thevideo encoder (403) in the FIG. 4 example.

The video encoder (603) may receive video samples from a video source(601) (that is not part of the electronic device (620) in the FIG. 6example) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) is a part ofthe electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (601) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (601) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (603) may code andcompress the pictures of the source video sequence into a coded videosequence (643) in real time or under any other time constraints asrequired. Enforcing appropriate coding speed is one function of acontroller (650). In some embodiments, the controller (650) controlsother functional units as described below and is functionally coupled tothe other functional units. The coupling is not depicted for clarity.Parameters set by the controller (650) can include rate control relatedparameters (picture skip, quantizer, lambda value of rate-distortionoptimization techniques, . . . ), picture size, group of pictures (GOP)layout, maximum motion vector search range, and so forth. The controller(650) can be configured to have other suitable functions that pertain tothe video encoder (603) optimized for a certain system design.

In some embodiments, the video encoder (603) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (630) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (633)embedded in the video encoder (603). The decoder (633) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create. The reconstructed sample stream (sample data)is input to the reference picture memory (634). As the decoding of asymbol stream leads to bit-exact results independent of decoder location(local or remote), the content in the reference picture memory (634) isalso bit exact between the local encoder and remote encoder. In otherwords, the prediction part of an encoder “sees” as reference picturesamples exactly the same sample values as a decoder would “see” whenusing prediction during decoding. This fundamental principle ofreference picture synchronicity (and resulting drift, if synchronicitycannot be maintained, for example because of channel errors) is used insome related arts as well.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5 . Brieflyreferring also to FIG. 5 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633).

In an embodiment, a decoder technology except the parsing/entropydecoding that is present in a decoder is present, in an identical or asubstantially identical functional form, in a corresponding encoder.Accordingly, the disclosed subject matter focuses on decoder operation.The description of encoder technologies can be abbreviated as they arethe inverse of the comprehensively described decoder technologies. Incertain areas a more detail description is provided below.

During operation, in some examples, the source coder (630) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously coded picture fromthe video sequence that were designated as “reference pictures.” In thismanner, the coding engine (632) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture memory (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by applying lossless compression to the symbolsaccording to technologies such as Huffman coding, variable lengthcoding, arithmetic coding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video encoder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (640) may transmit additional datawith the encoded video. The source coder (630) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions, are performedin the unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 7 shows an exemplary diagram of a video encoder (703). The videoencoder (703) is configured to receive a processing block (e.g., aprediction block) of sample values within a current video picture in asequence of video pictures, and encode the processing block into a codedpicture that is part of a coded video sequence. In an example, the videoencoder (703) is used in the place of the video encoder (403) in theFIG. 4 example.

In an HEVC example, the video encoder (703) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (703) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (703) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 7 example, the video encoder (703) includes an inter encoder(730), an intra encoder (722), a residue calculator (723), a switch(726), a residue encoder (724), a general controller (721), and anentropy encoder (725) coupled together as shown in FIG. 7 .

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also generate intraprediction information (e.g., an intra prediction direction informationaccording to one or more intra encoding techniques). In an example, theintra encoder (722) also calculates intra prediction results (e.g.,predicted block) based on the intra prediction information and referenceblocks in the same picture.

The general controller (721) is configured to determine general controldata and control other components of the video encoder (703) based onthe general control data. In an example, the general controller (721)determines the mode of the block, and provides a control signal to theswitch (726) based on the mode. For example, when the mode is the intramode, the general controller (721) controls the switch (726) to selectthe intra mode result for use by the residue calculator (723), andcontrols the entropy encoder (725) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(721) controls the switch (726) to select the inter prediction resultfor use by the residue calculator (723), and controls the entropyencoder (725) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (723) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (722) or the inter encoder (730). Theresidue encoder (724) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (724) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (703) also includes a residuedecoder (728). The residue decoder (728) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (722) and theinter encoder (730). For example, the inter encoder (730) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (722) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (725) is configured to format the bitstream toinclude the encoded block. The entropy encoder (725) is configured toinclude various information in the bitstream according to a suitablestandard, such as the HEVC standard. In an example, the entropy encoder(725) is configured to include the general control data, the selectedprediction information (e.g., intra prediction information or interprediction information), the residue information, and other suitableinformation in the bitstream. Note that, according to the disclosedsubject matter, when coding a block in the merge submode of either intermode or bi-prediction mode, there is no residue information.

FIG. 8 shows an exemplary diagram of a video decoder (810). The videodecoder (810) is configured to receive coded pictures that are part of acoded video sequence, and decode the coded pictures to generatereconstructed pictures. In an example, the video decoder (810) is usedin the place of the video decoder (410) in the FIG. 4 example.

In the FIG. 8 example, the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residue decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in FIG. 8 .

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode) and prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (872) or the inter decoder (880), respectively. Thesymbols can also include residual information in the form of, forexample, quantized transform coefficients, and the like. In an example,when the prediction mode is inter or bi-predicted mode, the interprediction information is provided to the inter decoder (880); and whenthe prediction type is the intra prediction type, the intra predictioninformation is provided to the intra decoder (872). The residualinformation can be subject to inverse quantization and is provided tothe residue decoder (873).

The inter decoder (880) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (872) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (873) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual informationfrom the frequency domain to the spatial domain. The residue decoder(873) may also require certain control information (to include theQuantizer Parameter (QP)), and that information may be provided by theentropy decoder (871) (data path not depicted as this may be low volumecontrol information only).

The reconstruction module (874) is configured to combine, in the spatialdomain, the residual information as output by the residue decoder (873)and the prediction results (as output by the inter or intra predictionmodules as the case may be) to form a reconstructed block, that may bepart of the reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (403), (603), and (703), and thevideo decoders (410), (510), and (810) can be implemented using anysuitable technique. In an embodiment, the video encoders (403), (603),and (703), and the video decoders (410), (510), and (810) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (403), (603), and (603), and the videodecoders (410), (510), and (810) can be implemented using one or moreprocessors that execute software instructions.

The disclosure includes embodiments related to scene detection basedencoding. For example, the scene detection based encoding can includeencoding methods related to pictures that are independent of otherpictures. For example, the encoding methods may be related to picturesthat are detected as camera flash pictures and/or inserted pictures.

ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC 1/SC 29/WG 11) published theH.265/HEVC (High Efficiency Video Coding) standard in 2013 (version 1),2014 (version 2), 2015 (version 3), and 2016 (version 4). In 2015, thetwo standard organizations jointly formed JVET (Joint Video ExplorationTeam) to explore the potential of developing a next video codingstandard beyond HEVC. In October 2017, the two standard organizationsissued the Joint Call for Proposals on Video Compression with Capabilitybeyond HEVC (CfP). By Feb. 15, 2018, 22 CfP responses on standarddynamic range (SDR), 12 CfP responses on high dynamic range (HDR), and12 CfP responses on 360 video categories were submitted, respectively.In April 2018, all received CP responses were evaluated in the 122MPEG/10th JVET meeting. As a result of the meeting, JVET formallylaunched a standardization process of next-generation video codingbeyond HEVC. The new standard was named Versatile Video Coding (VVC),and JVET was renamed as Joint Video Experts Team. In 2020, ITU-T VCEG(Q6/16) and ISO/IEC MPEG (JTC 1/SC 29/WG 11) published the VVC videocoding standard (version 1).

In inter prediction, for each inter-predicted coding unit (CU), motionparameters are required for coding features of VVC, for example, to beused for the inter-predicted sample generation. The motion parameterscan include motion vectors, reference picture indices, a referencepicture list usage index, and/or additional information. The motionparameters can be signaled in an explicit or implicit manner. When a CUis coded with a skip mode, the CU can be associated with one PU, and asignificant residual coefficient, a coded motion vector delta, and/or areference picture index may not be required. When a CU is coded with amerge mode, the motion parameters for the CU can be obtained fromneighboring CUs. The neighboring CUs can include spatial and temporalcandidates, and additional schedules (or additional candidates) such asintroduced in VVC. The merge mode can be applied to any inter-predictedCU, not only to skip mode. An alternative to the merge mode is anexplicit transmission of motion parameters, where a motion vector, acorresponding reference picture index for each reference picture list, areference picture list usage flag, and/or other needed information canbe signaled explicitly per CU.

In VVC, a VVC Test model (VTM) reference software can include a numberof new and refined inter prediction coding tools, which can include oneor more of the following:

(1) Extended merge prediction

(2) Merge motion vector difference (MMVD)

(3) Advanced Motion Vector Prediction (AMVP) mode with symmetric MVDsignalling

(4) Affine motion compensated prediction

(5) Subblock-based temporal motion vector prediction (SbTMVP)

(6) Adaptive motion vector resolution (AMVR)

(7) Motion field storage: 1/16^(th) luma sample MV storage and 8×8motion field compression

(8) Bi-prediction with CU-level weights (BCW)

(9) Bi-directional optical flow (BDOF)

(10) Decoder-side motion vector refinement (DMVR)

(11) Combined inter and intra prediction (CIIP)

(12) Geometric partitioning mode (GPM)

In Bi-prediction with CU-level weights (BCW), a bi-prediction signal,such as in HEVC, can be generated by averaging two prediction signalsobtained from two different reference pictures and/or using twodifferent motion vectors. In VVC, the bi-prediction mode can be extendedbeyond simple averaging to allow weighted averaging of the twoprediction signals. In an example, the weighted averaging of the twoprediction signals can be shown in equation (1)

P _(bi-pred)=((8−w)*P ₀ +w*P ₁+4)>>3  Eq. (1)

where w can be a weight, P₀ can be a first predictor, and P₁ can be asecond predictor, respectively. Five weights can be allowed in theweighted averaging bi-prediction, for example w ∈{−2, 3, 4, 5, 10}. Foreach bi-predicted CU, the weight w can be determined in one of two ways:(1) for a non-merge CU, a weight index can be signalled after the motionvector difference, or (2) for a merge CU, the weight index can beinferred from neighboring blocks based on a merge candidate index. BCWmay only be applied to CUs with 256 or more luma samples (e.g., CU widthtimes CU height is greater than or equal to 256). For low-delaypictures, all 5 weights can be used. For non-low-delay pictures, only 3weights (e.g., w∈ {3,4,5}) can be used.

At an encoder, fast search algorithms can be applied to find the weightindex without significantly increasing the encoder complexity. The fastsearch algorithms can be summarized as follows.

(1) when combined with AMVR, unequal weights may only be conditionallychecked for 1-pel and 4-pel motion vector precisions if the currentpicture is a low-delay picture.(2) when combined with affine, affine ME will be performed for unequalweights if and only if the affine mode is selected as the current bestmode.(3) when two reference pictures in bi-prediction are the same, unequalweights may only be conditionally checked.(4) unequal weights may not be searched when certain conditions are met,depending on the POC distance between the current picture and referencepictures of the current picture, a coding quantization parameter (QP),and a temporal level.

The BCW weight index can be coded using one context coded bin followedby bypass coded bins. A first context coded bin can indicate if equalweight is used. If an unequal weight is used, additional bins can besignalled using bypass coding to indicate which unequal weight is used.

Weighted prediction (WP), which can be processed in a picture level, canbe a coding tool supported by video standards, such as the H.264/AVC andHEVC standards, to efficiently code video content with fading. Supportfor WP can also be added into the VVC standard. WP can allow weightingparameters (e.g., a weight and an offset) to be signalled for eachreference picture in each of reference picture lists L0 and L1. Then,during motion compensation, the weight(s) and offset(s) of correspondingreference picture(s) can be applied. WP and BCW can be designed fordifferent types of video content. In order to avoid interactions betweenWP and BCW, which can complicate VVC decoder design, if a CU uses WP,then the BCW weight index may not be signalled, and w can be inferred tobe 4 (e.g., an equal weight is applied). For a merge CU, the weightindex can be inferred from neighboring blocks based on a merge candidateindex. The merge CU can be obtained based on one of a normal merge modeand an inherited affine merge mode. For a constructed affine merge mode,affine motion information can be constructed based on motion informationof up to 3 blocks. The BCW index for a CU using the constructed affinemerge mode can simply be set equal to the BCW index of a first controlpoint MV.

CIIP and BCW, such as in VVC, may not be jointly applied for a CU. Whena CU is coded with CIIP mode, the BCW index of the current CU can be setto 2, e.g., an equal weight.

Bi-directional optical flow (BDOF) in VVC, was previously referred to asBIO in the JEM. Compared to the JEM version, the BDOF in VVC can be asimpler version that requires less computation, especially in terms ofthe number of multiplications and the size of the multiplier.

BDOF can be used to refine a bi-prediction signal of a CU at a 4×4subblock level. In an example, BDOF can be applied to a CU if the CUsatisfies conditions as follows:

(1) The CU is coded using “true” bi-prediction mode, i.e., one of thetwo reference pictures is prior to the current picture in display orderand the other is after the current picture in display order,

(2) The distances (e.g., POC difference) from two reference pictures tothe current picture are the same,

(3) Both reference pictures are short-term reference pictures,

(4) The CU is not coded using affine mode or the SbTMVP merge mode,

(5) CU has more than 64 luma samples,

(6) Both CU height and CU width are larger than or equal to 8 lumasamples,

(7) BCW weight index indicates equal weight,

(8) Weighted position (WP) is not enabled for the current CU, and

(9) CIIP mode is not used for the current CU.

BDOF may be only applied to a luma component. As the name of BDOFindicates, the BDOF mode can be based on an optical flow concept, whichassumes that a motion of an object is smooth. For each 4×4 subblock, amotion refinement (v_(x), v_(y)) can be calculated by minimizing adifference between L0 and L1 prediction samples. The motion refinementcan then be used to adjust the bi-predicted sample values in the 4×4subblock. BDOF can include steps as follows:

First, horizontal and vertical gradients,

${\frac{\partial I^{(k)}}{\partial x}\left( {i,j} \right){and}\frac{\partial I^{(k)}}{\partial y}\left( {i,j} \right)},$

k=0,1, of the two prediction signals from the reference list L0 and thereference list L1 can be computed by directly calculating a differencebetween two neighboring samples. The horizontal and vertical gradientscan be provided in equations (2) and (3) as follows:

$\begin{matrix}{{\frac{\partial I^{(k)}}{\partial x}\left( {i,j} \right)} = \left( {\left( {{I^{(k)}\left( {{i + 1},j} \right)} \gg {{shift}1}} \right) - \left( {{I^{(k)}\left( {{i - 1},j} \right)} \gg {{shift}1}} \right)} \right)} & {{Eq}.(2)}\end{matrix}$ $\begin{matrix}{{\frac{\partial I^{(k)}}{\partial y}\left( {i,j} \right)} = \left( {\left( {{I^{(k)}\left( {i,{j + 1}} \right)} \gg {{shift}1}} \right) - \left( {{I^{(k)}\left( {i,{j - 1}} \right)} \gg {{shift}1}} \right)} \right)} & {{Eq}.(3)}\end{matrix}$

where l^((k))(i,j) can be a sample value at coordinate (i,j) of theprediction signal in list k, k=0,1, and shift1 can be calculated basedon a luma bit depth, bitDepth, as shift1=max(6, bitDepth−6).

Then, an auto- and cross-correlation of the gradients, S₁, S₂, S₃, S₅and S₆, can be calculated according to equations (4)-(8) as follows:

S ₁=Σ_((i,j)∈Ω)Abs(ψ_(x)(i,j)),  Eq. (4)

S ₂=Σ_((i,j)∈Ω)ψ_(x)(i,j)·Sign(ψ_(y)(i,j))  Eq. (5)

S ₃=Σ_((i,j)∈Ω)θ(i,j)·Sign(ψ_(x)(i,j))  Eq. (6)

S ₅=Σ_((i,j)∈Ω)Abs(ψ_(y)(i,j))  Eq. (7)

S ₆=Σ_((i,j)∈Ω)θ(i,j)·Sign(ψ_(y)(i,j))  Eq. (8)

where ψ_(x)(i,j), ψ_(y)(i,j), and θ(i,j) can be provided in equations(9)-(11) respectively.

$\begin{matrix}{{\psi_{x}\left( {i,j} \right)} = {\left( {{\frac{\partial I^{(1)}}{\partial x}\left( {i,j} \right)} + {\frac{\partial I^{(0)}}{\partial x}\left( {i,j} \right)}} \right) \gg n_{a}}} & {{Eq}.(9)}\end{matrix}$ $\begin{matrix}{{\psi_{y}\left( {i,j} \right)} = {\left( {{\frac{\partial I^{(1)}}{\partial y}\left( {i,j} \right)} + {\frac{\partial I^{(0)}}{\partial y}\left( {i,j} \right)}} \right) \gg n_{a}}} & {{Eq}.(10)}\end{matrix}$ $\begin{matrix}{{\theta\left( {i,j} \right)} = {\left( {{I^{(1)}\left( {i,j} \right)} \gg n_{b}} \right) - \left( {{I^{(0)}\left( {i,j} \right)} \gg n_{b}} \right)}} & {{Eq}.(11)}\end{matrix}$

where Ω can be a 6×6 window around the 4×4 subblock, and the values ofn_(a) and n_(b) can be set equal to min (1, bitDepth−11) and min (4,bitDepth−8), respectively.

The motion refinement (v_(x), v_(y)) can then be derived using thecross- and auto-correlation terms using equations (12) and (13) asfollows:

v _(x) =S ₁>0?clip3(−th _(BIO) ′,th _(BIO)′,−((S ₃·2^(n) ^(b) ^(−n) ^(a))>>└log₂ S ₁┘)):0  Eq. (12)

v _(y) =S _(s)>0?clip3(−th _(BIO) ′,th _(BIO)′,−((S ₆·2^(n) ^(b) ^(−n)^(a) )−((v _(x) S _(2,m))<<n _(s) ₂ +v _(x) S _(2,s))/2)>└log₂ S_(s)┘)):0  Eq. (13)

where S_(2,m)=S₂>>n_(S) ₂ , S_(2,s)=S₂&(2^(n)s₂ −1),th′_(BIO)=2^(max (S,BD−7)), └⋅┘ is a floor function, and n_(S) ₂ =12.Based on the motion refinement and the gradients, an adjustment can becalculated for each sample in the 4×4 subblock based on equation (14):

$\begin{matrix}{{b\left( {x,y} \right)} = {{rnd}\left( {\left( {{v_{x}\left( {\frac{\partial{I^{(1)}\left( {x,y} \right)}}{\partial x} - \frac{\partial{I^{(0)}\left( {x,y} \right)}}{\partial x}} \right)} + \text{ }{v_{y}\left( {\frac{\partial{I^{(1)}\left( {x,y} \right)}}{\partial y} - \frac{\partial{I^{(0)}\left( {x,y} \right)}}{\partial y}} \right)} + 1} \right)/2} \right)}} & {{Eq}.(14)}\end{matrix}$

Finally, the BDOF samples of the CU can be calculated by adjusting thebi-prediction samples in equation (15) as follows:

pred_(BDOF)(x,y)=(I ⁽⁰⁾(x,y)+I ⁽¹⁾(x,y)+b(x,y)+o _(offset))>>shift  Eq.(15)

Values can be selected such that multipliers in the BDOF process do notexceed 15-bits, and a maximum bit-width of the intermediate parametersin the BDOF process can be kept within 32-bits.

In order to derive the gradient values, some prediction samplesI^((k))(i,j) in the list k (k=0,1) outside of the current CU boundariesneed to be generated. As shown in FIG. 9 , BDOF in VVC can use oneextended row/column (902) around boundaries (906) of a CU (904). Inorder to control the computational complexity of generating theout-of-boundary prediction samples, prediction samples in an extendedarea (e.g., unshaded region in FIG. 9 ) can be generated by taking thereference samples at the nearby integer positions (e.g., using a floor() operation on the coordinates) directly without interpolation, and anormal 8-tap motion compensation interpolation filter can be used togenerate prediction samples within the CU (e.g., the shaded region inFIG. 9 ). The extended sample values can be used in gradient calculationonly. For the remaining steps in the BDOF process, if any samples andgradient values outside of the CU boundaries are needed, the samples andgradient values can be padded (e.g., repeated) from nearest neighbors ofthe samples and gradient values.

When a width and/or a height of a CU is larger than 16 luma samples, theCU can be split into subblocks with a width and/or a height equal to 16luma samples, and the subblock boundaries can be treated as CUboundaries in the BDOF process. A maximum unit size for a BDOF processcan be limited to 16×16. For each subblock, the BDOF process can beskipped. When a sum of absolute difference (SAD) between the initial L0and L1 prediction samples is smaller than a threshold, the BDOF processmay not be applied to the subblock. The threshold can be set equal to(8*W*(H>>1), where W can indicate the width of the subblock, and H canindicate the height of the subblock. To avoid the additional complexityof a SAD calculation, the SAD between the initial L0 and L1 predictionsamples calculated in DMVR process can be re-used in the BBOF process.

If BCW is enabled for a current block, i.e., the BCW weight indexindicates unequal weighting, then bi-directional optical flow can bedisabled. Similarly, if WP is enabled for the current block, i.e., aluma weight flag (e.g., luma_weight_lx_flag) is 1 for either of the tworeference pictures, then BDOF may also be also disabled. When a CU iscoded with symmetric MVD mode or CIIP mode, BDOF may also be disabled.

In order to increase the accuracy of the MVs of the merge mode, abilateral-matching (BM)-based decoder side motion vector refinement canbe applied, such as in VVC. In a bi-prediction operation, a refined MVcan be searched around initial MVs in a reference picture list L0 and areference picture list L1. The BM method can calculate a distortionbetween two candidate blocks in the reference picture list L0 and listL1.

FIG. 10 shows an exemplary schematic view of a BM-based decoder sidemotion vector refinement. As show in FIG. 10 , a current picture (1002)can include a current block (1008). The current picture can include areference picture list L0 (1004) and a reference picture list L1 (1006).The current block (1008) can include an initial reference block (1012)in the reference picture list L0 (1004) according to an initial motionvector MV0 and an initial reference block (1014) in the referencepicture list L1 (1006) according to an initial motion vector MV1. Asearching process can be performed around the initial MV0 in thereference picture list L0 (1004) and the initial MV1 in the referencepicture list L1 (1006). For example, a first candidate reference block(1010) can be identified in the reference picture list L0 (1004) basedon a candidate motion vector MV0′ around the initial MV0, and a firstcandidate reference block (1016) can be identified in the referencepicture list L1 (1006) based on a candidate motion vector MV1′ aroundthe initial MV1. A SAD between a pair of candidate reference blocks inthe reference picture list L0 and the reference picture list L1 can becalculated. For example, a SAD can be calculated for the first candidatereference block (1010) in the first reference picture list L0 and thefirst candidate reference block (1016) in the reference picture list L1.MV candidates associated with the lowest SAD can become the refined MVsand used to generate a bi-predicted signal to predict the current block(1008).

In an example. the application of DMVR can be restricted and may only beapplied for CUs which are coded based on modes and features, such as inVVC, as follows:

(1) CU level merge mode with bi-prediction MV,

(2) One reference picture is in the past and another reference pictureis in the future with respect to the current picture,

(3) The distances (e.g., POC difference) from two reference pictures tothe current picture are the same,

(4) Both reference pictures are short-term reference pictures,

(5) CU has more than 64 luma samples,

(6) Both CU height and CU width are larger than or equal to 8 lumasamples,

(7) BCW weight index indicates equal weight,

(8) WP is not enabled for the current block, and

(9) CIIP mode is not used for the current block.

The refined MV derived by the DMVR process can be used to generate interprediction samples and be used in temporal motion vector prediction forfuture pictures coding. While the original MV can be used in thedeblocking process and be used in spatial motion vector prediction forfuture CU coding.

In DVMR, search points can surround the initial MV and the MV offset canobey a MV difference mirroring rule. In other words, any points that arechecked by DMVR, denoted by a candidate MV pair (MV0, MV1), can obey theMV difference mirroring rule that is shown in equations (16) and (17):

MV0′=MV0+MV_offset  Eq. (16)

MV1′=MV1−MV_offset  Eq. (17)

Where MV_offset can represent a refinement offset between the initial MVand the refined MV in one of the reference pictures. The refinementsearch range can be two integer luma samples from the initial MV. Thesearching can include an integer sample offset search stage and afractional sample refinement stage.

For example, a 25 points full search can be applied for integer sampleoffset searching. The SAD of the initial MV pair can first becalculated. If the SAD of the initial MV pair is smaller than athreshold, the integer sample stage of DMVR can be terminated. OtherwiseSADs of the remaining 24 points can be calculated and checked in ascanning order, such as a raster scanning order. The point with thesmallest SAD can be selected as an output of an integer sample offsetsearching stage. To reduce the penalty of the uncertainty of DMVRrefinement, the original MV during the DMVR process can have a priorityto be selected. The SAD of the reference blocks referred to by theinitial MV candidates can be decreased by ¼ of the SAD value.

The integer sample search can be followed by a fractional samplerefinement. To save calculational complexity, the fractional samplerefinement can be derived by using a parametric error surface equation,instead of an additional search with a SAD comparison. The fractionalsample refinement can be conditionally invoked based on the output ofthe integer sample search stage. When the integer sample search stage isterminated with a center having the smallest SAD in either the firstiteration search or the second iteration search, the fractional samplerefinement can further be applied.

In a parametric error surface-based sub-pixel offsets estimation, thecenter position cost and the costs at four neighboring positions fromthe center can be used to fit a 2-D parabolic error surface equationbased on equation (18):

E(x,y)=A(x−x _(min))² +B(y−y _(min))² +C  Eq. (18)

where (x_(min), y_(min)) can correspond to a fractional position withthe least cost and C can correspond to a minimum cost value. By solvingthe equation (18) using the cost value of the five search points, the(x_(min),y_(min)) can be computed in equations (19) and (20):

x _(min)=(E(−1,0)−E(1,0))/(2(E(−1,0)+E(1,0)−2E(0,0)))  Eq. (19)

y _(min)=(E(0,−1)−E(0,1))/(2((E(0,−1)+E(0,1)−2E(0,0)))  Eq. (20)

The value of x_(min) and y_(min) can be automatically constrained to bebetween −8 and 8 since all cost values are positive and the smallestvalue is E(0,0). The constraints of the value of x_(min) and y_(min) cancorrespond to a half pel (or pixel) offset with 1/16th-pel MV accuracyin VVC. The computed fractional (x_(min), y_(min)) can be added to theinteger distance refinement MV to get the sub-pixel accurate refinementdelta MV.

Bilinear-interpolation and sample padding can be applied, such as inVVC. A resolution of MVs can be 1/16 luma samples, for example. Samplesat a fractional position can be interpolated using an 8-tapinterpolation filter. In DMVR, search points can surround an initialfractional-pel MV with an integer sample offset, therefore the samplesof the fractional position need to be interpolated for a DMVR searchprocess. To reduce calculational complexity, a bi-linear interpolationfilter can be used to generate the fractional samples for the searchingprocess in DMVR. In another important effect, by using the bi-linearfilter with a 2-sample search range, the DVMR does not access morereference samples compared to a normal motion compensation process.After the refined MV is attained with a DMVR search process, the normal8-tap interpolation filter can be applied to generate a finalprediction. In order not to access more reference samples compared to anormal MC process, the samples, which may not be needed for theinterpolation process based on the original MV but may be needed for theinterpolation process based on the refined MV, can be padded fromsamples that are available.

When a width and/or a height of a CU is larger than 16 luma samples, theCU can be further split into subblocks with a width and/or a heightequal to 16 luma samples. A maximum unit size for DMVR searching processcan be limited to 16×16.

Motion Compensated Temporal Filtering (MCTF) may be used as apreprocessing tool in various encoders. For example, VTM (VVC referencesoftware) can use a temporal filter (TF) to increase similarity betweena current frame and neighbor frames of the current fame so that residualinformation can be reduced. The term TF frame can be used to denote aframe to be filtered by the temporal filter. TF can be applied for eachpicture at an interval POC of 16 or 8. Up to 4 references in a forwardand a backward direction can be used to derive a weight for bilateralfiltering. Original samples of TF frames at a kth spatial location canbe filtered as described in equation (21)

$\begin{matrix}{{I_{n}(k)} = \frac{{I_{o}(k)} + {\Sigma_{i = 0}^{7}{w_{r}\left( {i,a,k} \right)}{I_{r}\left( {i,k} \right)}}}{1 + {\Sigma_{i = 0}^{7}{w_{r}\left( {i,a,k} \right)}}}} & {{Eq}.(21)}\end{matrix}$

where, I_(n)(k) and I_(o)(k) can represent a filtered pixel (or filteredpixel value) and an original pixel (or original pixel value) of a pixeli in a current picture at a spatial location k, respectively. k can bethe location of the pixel i in the current picture. I_(r)(i,k) candenote a collocated pixel (or collocated pixel value) in a neighboringpicture I_(r) for the pixel i in the current picture. The collocatedpixel can also be located at a kth spatial location of the neighboringpicture I_(r) which is at a rth motion compensated reference frame. Theneighboring picture I_(r) can be derived by performing motion estimationand then motion compensation from the reference frame r to the currentTF picture. A weight for each reference (or pixel) i in a number ofavailable reference pictures at the spatial location k, w_(r)(i,a,k),can be derived as follows in equation (22) for a luma sample:

$\begin{matrix}{{w_{r}\left( {i,a,k} \right)} = {b{w \cdot s_{o} \cdot {s_{r}\left( {i,a} \right)} \cdot e^{- \frac{\Delta{I({i,k})}^{2}}{s{w \cdot {\sigma_{i}({QP})}^{2}}}}}}} & {{Eq}.(22)}\end{matrix}$

where, bw=0.4 stands for a base weight, s₀ is a basic filter strengthdecided by an interval POC as described in equation (23)

$\begin{matrix}{s_{0} = \left\{ \begin{matrix}1.5 & {{{if}{POC}{\% 16}} = 0} \\0.95 & {{{if}{POC}{\% 8}} = 0}\end{matrix} \right.} & {{Eq}.(23)}\end{matrix}$

A reference filter strength, s_(r)(i,a), can be defined by a look uptable depending on whether references are available in both directions(a=8 references) or one direction (a=4 references). s_(r)(i,a) can bedescribed in equation (24) as follows:

$\begin{matrix}{{s_{r}\left( {i,4} \right)} = \left\{ {\begin{matrix}\begin{matrix}\begin{matrix}1.13 \\0.97\end{matrix} \\0.81\end{matrix} \\0.57\end{matrix},{{{and}{s_{r}\left( {i,8} \right)}} = \left\{ \begin{matrix}\begin{matrix}\begin{matrix}\begin{matrix}\begin{matrix}\begin{matrix}\begin{matrix}0.33 \\0.41\end{matrix} \\0.57\end{matrix} \\0.85\end{matrix} \\0.85\end{matrix} \\0.57\end{matrix} \\0.41\end{matrix} \\0.33\end{matrix} \right.}} \right.} & {{Eq}.(24)}\end{matrix}$

ΔI(i,k) can represent a pixel difference between the original pixel atthe spatial location k and the collocated pixels of the original pixelif the original pixel is at a ith reference picture. sw can denote asigma base weight of 2. σ_(i)(QP)=3*(QP−10) when QP is a slice QP. Thebase weight bw and the sigma weight sw can further be adjustedadaptively for each 8×8 block based on a block error and a simple blockfrequency weighting.

Scene cut detection may include a technique for detecting whether anabrupt scene transition occurs, for example when content changes fromone scene to another scene. A scene change can result in a significantchange in content, and can detected for example by evaluating adifference between temporally neighboring pictures.

Flash detection may include a technique for detecting whether one ormore pictures are significantly different from other pictures in asequence of pictures of one scene, such as due to a camera flash, orinsertion of picture(s) during video editing. The flash detection can beperformed in a similar way as scene cut detection, for example. Flashdetection may be performed to determine whether past and futureneighboring frames belong to a same scene.

FIG. 11 shows a schematic illustration of an example of flash picturedetection. As shown in FIG. 11 , a sequence of pictures includingpictures (1102), (1104), (1106), (1108), (1110), (1112), (1114),(11116), and (1118) can be provided. The picture (1110) in the sequenceof pictures can be detected as a flash picture when the picture (1110)belongs to a first scene (e.g., scene 1), and the pictures (1102),(1104), (1106), and (1108) that are prior to the picture (1110) and thepictures (1112), (1114), (1116), and (1118) that are subsequent to thepicture (1110) belong to a second scene (e.g., scene 0).

Fade detection can include a technique to detect whether a group ofconsecutive pictures are in the middle of a gradual transition from onescene to another. Some special cases may include transitioning into orout of a blank picture with one color, such as black or white. Ahistogram of pictures can be utilized to perform the fade detection.

Noise estimation can include a common technique in image processing,where a noise level can often be estimated via evaluating a gradientenergy of a picture. Local contents like edges, smooth areas, ortextures can be further utilized to derive the noise level with a higheraccuracy.

In an example, a noise detection process can be shown in FIG. 12 . Asshown in FIG. 12 , at (1202), a Sobel operation can be used for edgedetection to exclude edges from noise detection.

According to the Sobel operation, a current picture can be denoted asI(x,y), where (x,y) is a coordinate of a pixel. An output of the Sobeloperator can be described in equation (25) as follows:

$\begin{matrix}{G = {{❘{{I\left( {x,y} \right)}*\begin{bmatrix}{- 1} & {- 2} & {- 1} \\0 & 0 & 0 \\1 & 2 & 1\end{bmatrix}}❘} + {❘{{I\left( {x,y} \right)}*\begin{bmatrix}{- 1} & 0 & 1 \\{- 2} & 0 & 2 \\{- 1} & 0 & 1\end{bmatrix}}❘}}} & {{Eq}.(25)}\end{matrix}$

where |⋅| defines an absolute operator. An edge map can be determinedusing a threshold G_(th) for G. At (1202), pixels with G<G_(th) can beused in the noise detection with a Laplacian operator. At (1204), anoise level calculation can be described in equation (26).

$\begin{matrix}{\sigma = {\sqrt{\frac{\pi}{2}}\frac{1}{6\left( {W - 2} \right)\left( {H - 2} \right)}{\sum_{x,y}{❘{{I\left( {x,y} \right)}*N}❘}}}} & {{Eq}.(26)}\end{matrix}$

where N can be a Laplacian operator according to equation (27).

$\begin{matrix}{N = \begin{bmatrix}1 & {- 2} & 1 \\{- 2} & 4 & {- 2} \\1 & {- 2} & 1\end{bmatrix}} & {{Eq}.(27)}\end{matrix}$

Sample content, such as a blank screen, can be easily detected for ablock with B×B pixels by comparing a pixel variance and/or a pixel valuerange (e.g., max_pixel_val−min_pixel_val).

To reduce computational complexity, down-sampled pictures can be usedfor pre-analysis of a video sequence in video encoders. In an example, apre-analysis picture can be down sampled with a 1:2 ratio bothvertically and horizontally from an original full-sized picture, whichcan result in a down-sampled pre-analysis picture with ¼ of the numberof pixels as in the original picture.

In some cases, the down-sampled pictures can be stored along with theoriginal picture, for example until the original picture is no longerneeded in the encoding process.

A coding tool called luma mapping with chroma scaling (LMCS) can beadded as a new processing block before the loop filters, such as in VVC.LMCS can have two main components: (1) in-loop mapping of a lumacomponent based on adaptive piecewise linear models, and (2) for chromacomponents, luma-dependent chroma residual scaling can be applied. FIG.13 shows a LMCS architecture (1300) from a perspective of a decoder. Asshown in FIG. 13 , blocks (1301)-(1303) can indicate a mapped domain inwhich the LMCS is applied. The block (1301) can include an inversequantization and an inverse transform, the block (1303) can include aluma intra prediction, and the block (1302) can include a reconstructionprocess to add a luma prediction with a luma residual. Blocks(1304)-(1311) can be an original (or non-mapped) domain in which theLMCS is applied. The original domain can include loop filters (e.g.,(1305) and (1310)) that can include deblocking, ALF, and SAO, motioncompensated prediction (e.g., (1304) and (1309)), chroma intraprediction (e.g., 1308)), adding of the chroma prediction together withthe chroma residual (e.g., (1307)), and storage of decoded pictures asreference pictures (e.g., (1311) and (1306)). Blocks (1312)-(1314) caninclude LMCS functional blocks. Block (1312) can include forward mappingof a luma signal, block (1313) can include inverse mapping of the lumasignal, and block (1314) can include a luma-dependent chroma scalingprocess. Like other tools in VVC, LMCS can be enabled/disabled at asequence level using an SPS flag.

In a luma mapping with a piecewise linear model, in-loop mapping of aluma component can adjust a dynamic range of an input signal byredistributing codewords across the dynamic range to improve compressionefficiency. Luma mapping can make use of a forward mapping function,FwdMap, and a corresponding inverse mapping function, InvMap. The FwdMapfunction can be signaled using a piecewise linear model with 16 equalpieces. The InvMap function may not need to be signaled, and may bederived from the FwdMap function.

The luma mapping model can be signaled in an adaptation parameter set(APS) syntax structure with an APS parameter type (e.g.,aps_params_type) being set equal to 1 (or 1 LMCS_APS). Up to 4 LMCS APScan be used in a coded video sequence. Only 1 LMCS APS can be used for apicture. The luma mapping model can be signaled using a piecewise linearmodel. The piecewise linear model can partition the dynamic range of theinput signal into 16 equal pieces. For each piece, linear mappingparameters of the respective piece can be expressed using the number ofcodewords assigned to the respective piece. Using 10-bit input as anexample, each of the 16 pieces can have 64 codewords assigned to therespective piece by default. The signaled number of the codewords can beused to calculate a scaling factor and adjust the mapping functionaccordingly for the corresponding piece. At the slice level, an LMCSenable flag can be signaled to indicate if the LMCS process shown inFIG. 13 can be applied to a current slice. If LMCS is enabled for thecurrent slice, an APS identity (e.g., aps_id) can be signaled in a sliceheader to identify an APS that carries the luma mapping parameters ofthe LMCS process.

Each i-th piece, i=0 . . . 15, of the FwdMap piecewise linear model canbe defined by two input pivot points InputPivot[ ] and two output(mapped) pivot points MappedPivot[ ]. The InputPivot[ ] and MappedPivot[] can be computed as follows (assuming 10-bit video):

 1) OrgCW = 64  2) For i = 0:16, InputPivot[ i ] = i * OrgCW  3) Fori=0:16, MappedPivot[i] is calculated as follows: MappedPivot[ 0 ] = 0;for( i = 0; i <16 ; i++)  MappedPivot[ i + 1 ] = MappedPivot[ i ] + SignalledCW[ i ] where SignalledCW[ i ] can be the signaled number ofcodewords for the i-th piece.

As shown in FIG. 13 , for an inter-coded block, motion compensatedprediction can be performed in the mapped domain. In other words, afterthe motion-compensated prediction block Y_(pred) is calculated based onthe reference signals in the DPB (e.g., (1306)), the FwdMap function(1312) can be applied to map the luma prediction block in the originaldomain to the mapped domain, Y′_(pred)=FwdMap(Y_(pred)). For anintra-coded block, the FwdMap function may not be applied because intraprediction can be performed in the mapped domain. After a reconstructedblock Y, is calculated, such as in block (1302), the InvMap function(1313) can be applied to convert the reconstructed luma values in themapped domain back to the reconstructed luma values in the originaldomain (Ŷ_(i)=InvMap(Y_(r))). The InvMap function can be applied to bothintra- and inter-coded luma blocks.

The luma mapping process (forward and/or inverse mapping) can beimplemented using either look-up tables (LUT) or using on-the-flycomputation. If a LUT is used, FwdMapLUT and InvMapLUT can bepre-calculated and pre-stored for use at the tile group level, andforward and inverse mapping can be simply implemented asFwdMap(Y_(pred))=FwdMapLUT[Y_(pred)] and InvMap(Y_(r))=InvMapLUT[Y_(r)],respectively. Alternatively, on-the-fly computation may be used. Usingforward mapping function FwdMap as an example, in order to figure outwhich piece includes a luma sample, a sample value of the luma samplecan be right-shifted by 6 bits (which corresponds to 16 equal pieces).Then, the linear model parameters for the corresponding piece can beretrieved and applied on-the-fly to compute the mapped luma value. Wheni is a piece index, a1, a2 are InputPivot[i] and InputPivot[i+1],respectively, and b1, b2 are MappedPivot[i] and MappedPivot[i+1],respectively, the FwdMap function can be evaluated as follows inequation (28):

FwdMap(Y _(pred))=((b2−b1)/(a2−a1))*(Y _(pred) −a1)+b1  Eq. (28)

The InvMap function can be computed on-the-fly in a similar manner.Generally, pieces in the mapped domain may not be equal sized.Therefore, a most straightforward inverse mapping process can requirecomparisons in order to figure out which piece of the pieces in themapped domain can include the current sample value. Such comparisons canincrease decoder complexity. Therefore, a bistream constraint can beimposed on the values of the output pivot points MappedPivot[i] asfollows: assume a range of the mapped domain (for 10-bit video, therange can be [0, 1023]) is divided into 32 equal pieces. IfMappedPivot[i] is not a multiple of 32, then MappedPivot[i+1] andMappedPivot[i] may not belong to the same piece of the 32 equal-sizedpieces, e.g., MappedPivot[i+1]>>(BitDepth_(Y)−5) may not be equal toMappedPivot[i]>>(BitDepth_(Y)−5). Based on the bitstream constraint, theInvMap function can also be carried out using a simple right bit-shiftby 5 bits (which corresponds 32 equal-sized pieces) in order to figureout which piece include the current sample value.

In luma-dependent chroma residual scaling, chroma residual scaling canbe designed to compensate for an interaction between a luma signal andcorresponding chroma signals of the luma signal. Whether the chromaresidual scaling is enabled or not can also be signaled at a slicelevel. If luma mapping is enabled, an additional flag can be signaled toindicate if luma-dependent chroma residual scaling is enabled or not.When luma mapping is not used, luma-dependent chroma residual scalingcan be disabled. Further, luma-dependent chroma residual scaling may bedisabled for chroma blocks that include an area less than or equal to 4.

Chroma residual scaling can depend on an average value of top and/orleft reconstructed neighboring luma samples of a current virtualpipeline data unit (VPDU). If a current CU is one of inter 128×128,inter 128×64, or inter 64×128, then a chroma residual scaling factorderived for the CU associated with a first VPDU can be used for allchroma transform blocks in the CU. Denote avgYr as an average of thereconstructed neighboring luma samples that are shown in block (1314) inFIG. 13 . The value of C_(ScaleInv) can be computed in steps as follows:

-   -   1) Find the index Y_(Idx) of the piecewise linear model to which        avgYr belongs based on the InvMap function.    -   2) C_(ScaleInv)=C_(ScaleInv) [Y_(Idx)], where C_(ScaleInv) [ ]        is a 16-piece LUT pre-computed based on the value of        SignalledCW[i] and a offset value signaled in APS for chroma        residual scaling process.        Unlike luma mapping, which is performed on the sample basis,        C_(ScaleInv) can be a constant value for the entire chroma        block. Based on C_(ScaleInv), chroma residual scaling can be        applied as follows in equations (29) and (30):

Encoder side: C _(ResScale) =C _(Res) *C _(Scale) =C _(Res) /C_(ScaleInv)  Eq. (29)

Decoder side: C _(Res) =C _(ResScale) /C _(Scale) =C _(ResScale) *C_(ScaleInv)  Eq. (30)

Results of scene transition detection can be used to optimize encodingperformance, such as assisting rate control and/or coding tooladjustment. Scene transition detection can also be used to improveencoding speed. An abrupt change in the content, for example from acamera flash picture or an inserted picture, may reduce the performanceof an inter picture prediction and/or temporal filtering. Other codingtools may also get affected by the abrupt content change.

In the disclosure, flash detection based encoding methods can beprovided to detect flash pictures in a sequence of pictures, where ascene change can be detected between the flash pictures and neighboringpictures of the flash pictures. For example, the flash pictures and theneighboring pictures can have different contents (e.g., contrasts,features, or objects). In some embodiments, both camera flash pictures,inserted pictures, or other pictures with an abrupt change in content,can be referred to as flash pictures. In some embodiments, a flashpicture (e.g., a camera flash picture) and neighboring pictures of theflash picture can belong to a same scene, but the flash picture and theneighboring pictures can have different contrasts which may beconsidered a scene change for the purpose of detecting a flash picturein some embodiments. In some embodiments, a flash picture (e.g., aninserted picture) can be a picture that belongs to a first scene, and aprevious neighboring picture and a past neighboring picture of thepicture can belong to a second scene. The first scene can be differentfrom the second scene. For example, the first scene and the second scenecan include different features or different objects. In someembodiments, whether a picture is a flash picture can be determinedbased on a scene change between (i) a first scene of the picture in asequence of pictures and (ii) a second scene of a prior picture and asubsequent picture of the picture in the sequence of pictures. The scenechange can be detected based on a content change between the first sceneand the second scene being larger than a threshold. For example, asshown in FIG. 14 , a picture (1404) can be determined as a flash picturebecause the picture (1404) belongs to a first scene that is differentfrom a second scene of a prior picture (1402) and a subsequent picture(1406) of the picture (1404). As described above, the scene change canbe detected based on one or more content changes, which can include atleast one of a feature or contrast change for example.

In some embodiments, an encoding processing, such as at least one of atemporal filter process or an encoding process, can be performed on acurrent picture in a sequence of pictures based on (i) whether thepicture is determined as a flash picture and (ii) whether the picture isthe current picture.

In the disclosure, flash pictures can be excluded from or in one or morecertain encoding processes. For example, flash pictures may be excludedin the temporal filtering process.

In an embodiment, based on a picture being determined as the flashpicture and being a current picture, the picture can be excluded in thetemporal filtering process.

In another embodiment, if a picture is detected as flash picture, thepicture may not be used as a reference picture. For example, the picturemay not be used in the temporal filtering process for a current picture.

In an example, the detected flash picture(s) in a reference range for atemporal filter of the temporal filtering process can be excluded andonly remaining reference pictures in the reference range can be used.For example, only the remaining reference pictures in the referencerange may be used for the temporal filtering process. In the exampleshown in FIG. 14 , based on the picture (1404) being detected as theflash picture, the picture (1404) can be excluded for the temporalfilter, and only remaining reference pictures (1402), (1406), and (1408)in the reference range 0 can be used for the temporal filtering process.

In an example, a reference range (or temporal filter reference range)can include N pictures on a temporal side of a current picture. When thereference range includes a flash picture or multiple flash pictures onthe temporal side, the temporal filter reference range can be extendedto include one or more non-flash reference pictures to maintain a numberof pictures as N on the temporal side, unless no additional referencepictures are available due to other restrictions. For example, as shownin FIG. 14 , the picture (1404) can be included in a reference range 0and positioned on a left temporal side with respect to a current picture(1410) (or a temporal side prior to the current picture (1410)). Whenthe picture (1404) is detected as a flash picture, the reference range 0can extend toward a temporal direction prior to the picture (1402) toinclude one more non-flash picture. Thus, a total number of thenon-flash reference pictures in the reference range 0 remains constant,such as 4 shown in FIG. 14 .

In the disclosure, special handling of inter predictions and codingtools on flash pictures can be provided, such as in an encoder side. Forexample, an encoder can determine or label a flash picture and thenperform one or more encoding processes based on the determined flashpicture.

In an embodiment, when a picture is detected as a flash picture, thepicture may be set as non-reference picture for a current picture in aprediction, such as an inter prediction.

In an embodiment, when a picture is detected as a flash picture, thepicture can be moved to a higher temporal level (or temporal layer) in agroup of pictures (GOP). The temporal level can indicate a hierarchylevel in which a picture in a lower level can be applied to predict apicture in a higher level.

In an embodiment, when a picture is detected as a flash picture, a slicetype in the picture can be changed. For example, the slice type of thepicture can be set as a P slice.

In an embodiment, when a picture is detected as a flash picture, a costestimation of a picture level weighted prediction (e.g., weightedprediction (WP)) can be added in the encoding process for the picture.In the cost estimation, a difference between a current picture and aprediction of the current picture can be calculated. The prediction canbe obtained based on a weighted combination of the flash picture andanother reference picture of the current picture.

In an embodiment, when a reference picture of a current picture isdetected as a flash picture, and the current picture is a B picture withtwo reference picture lists, some bi-prediction tools, such as BDOFand/or DMVR, may be disabled at a picture level. In an example,disabling of the bi-prediction tools can be signaled in a pictureheader.

In an embodiment, when a picture is detected as a flash picture and aLMCS tool is enabled, the LMCS tool may be disabled for the picture at apicture level or a slice level. Accordingly, a rate-distortionoptimization search based on the LMCS can be skipped for the picture onthe encoder.

In an embodiment, when a picture is detected as a flash picture and theLMCS tool is enabled and applicable to the picture, LMCS pictureanalysis can be performed for the picture to determine a new set of LMCSparameters that are different from LMCS parameters for non-flashpictures. For example, the new set of LMCS parameters can be a set ofnew linear mapping parameters. The new set of LMCS parameters can befurther applied to the flash picture for the LMCS process.

In an embodiment, when a picture is detected as a flash picture and theLMCS tool is enabled and applicable to the picture, a pre-defined set ofLMCS parameters for a flash scene can be checked on the encoder sidewhen an on/off decision is made for LMCS. The LMCS parameters for theflash scene may be associated with the picture in some embodiments, forexample different LMCS parameters may be associated with different typesof flash scenes. In an example, the pre-defined set of LMCS parametercan be generated by training general flash pictures. The general flashpictures can be sample flash pictures associated with content changes,contrast changes, or scene changes. In an example, the pre-defined LMCSparameters can be signaled in a particular APS. The particular APS canbe reserved for the pre-defined LMCS parameters.

FIG. 15 shows a flow chart outlining an exemplary encoding process(1500) according to some embodiments of the disclosure. The process (orembodiment) may be implemented by processing circuitry (e.g., one ormore processors or one or more integrated circuits). In one example, theone or more processors execute a program that is stored in anon-transitory computer-readable medium.

The process (e.g., (1500)) can be used in the encoding of a block, so asto generate a prediction block for the block. In various embodiments,the process (e.g., (1500)) is executed by processing circuitry, such asthe processing circuitry in the terminal devices (310), (320), (330) and(340), the processing circuitry that performs functions of the videoencoder (403), the processing circuitry that performs functions of thevideo encoder (603), and the like. In some embodiments, the process(e.g., (1500)) is implemented in software instructions, thus when theprocessing circuitry executes the software instructions, the processingcircuitry performs the process (e.g., (1500)).

As shown in FIG. 15 , the process (1500) can start from (S1501) andproceed to (S1510). At (S1510), whether a sequence of pictures includesa flash picture can be determined. The flash picture can be associatedwith a scene change between (i) a first scene of a picture of thesequence of pictures and (ii) a second scene of a prior picture and asubsequent picture of the picture in the sequence of pictures. The scenechange can be determined based on a content change between the firstscene and the second scene being larger than a threshold.

At (S1520), an encoding process can be performed on a current picture inthe sequence of pictures in response to (i) the picture being determinedas the flash picture and (ii) the picture being the current picture.

In an example, the picture can be determined as the flash picture basedon a contrast difference between the first scene and the second scenebeing larger than the threshold. In an example, the picture can bedetermined as the flash picture based on a feature difference betweenthe first scene and the second scene being larger than the threshold.

When the encoding process includes the temporal filter process, thetemporal filter process may not be performed on the picture based on thepicture being determined as the flash picture and being the currentpicture.

When the encoding process includes a temporal filter process, thepicture can be excluded as a reference picture in the temporal filterprocess based on the picture being determined as the flash picture andnot being the current picture.

In response to the picture being excluded as the reference picture inthe temporal filter process, another picture can be added to thesequence of pictures as a reference picture for the temporal filterprocess. Thus, a total number of reference pictures for the temporalfilter process can remain constant. The other picture and the picturecan be positioned at a same temporal side of the current picture in thetemporal filter process.

The encoding process can include one of an attribute adjustment, a costestimation, or a luma mapping with chroma scaling (LMCS) process. TheLMCS process can include in-loop mapping of a luma component of thecurrent picture and a scaling of a luma-dependent chroma residual of thecurrent picture.

When the encoding process includes the attribute adjustment, the picturecan be moved to a higher temporal level in the sequence of picturesbased on the picture being the flash picture.

When the encoding process includes the attribute adjustment, a slicetype of the picture can be set as a P slice based on the picture beingthe flash picture.

When the encoding process includes the attribute adjustment, the picturecan be determined as a non-reference picture of the current picturebased on the picture being the flash picture and not being the currentpicture.

When the encoding process includes the cost estimation, the costestimation can be performed to generate a difference between the currentpicture and a prediction that is based on a weighted combination of thepicture and another reference picture of the current picture based onthe picture being determined as the flash picture and not being thecurrent picture.

In some embodiments, at least one of bi-direction optical flow (BDOF) ordecoder side motion vector refinement (DMVR) can be disabled for thecurrent picture in the encoding process in response to (i) the picturebeing determined as the flash picture and being a reference picture ofthe current picture, and (ii) the current picture being a B type picturewith two reference picture lists.

When the encoding process includes the LMCS process, the LMCS processcan be disabled for the picture based on the picture being determined asthe flash picture.

When the encoding process includes the LMCS process, based on thepicture being determined as the flash picture, a set of LMCS parameterscan be determined for the picture based on an LMCS picture analysis. TheLMCS can be performed on the picture based on the determined set of LMCSparameters.

When the encoding process includes the LMCS process, the LMCS can beperformed on the picture based on a predefined set of LMCS parameters inresponse to the picture being determined as the flash picture. Thepredefined set of LMCS parameters can be generated by training aplurality of general flash pictures.

After (S1520), the process proceeds to (S1599) and terminates.

The process (1500) can be suitably adapted. Step(s) in the process(1500) can be modified and/or omitted. Additional step(s) can be added.Any suitable order of implementation can be used.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 16 shows a computersystem (1600) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 16 for computer system (1600) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1600).

Computer system (1600) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1601), mouse (1602), trackpad (1603), touchscreen (1610), data-glove (not shown), joystick (1605), microphone(1606), scanner (1607), camera (1608).

Computer system (1600) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1610), data-glove (not shown), or joystick (1605), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1609), headphones(not depicted)), visual output devices (such as screens (1610) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability-some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1600) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1620) with CD/DVD or the like media (1621), thumb-drive (1622),removable hard drive or solid state drive (1623), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1600) can also include an interface (1654) to one ormore communication networks (1655). Networks can for example bewireless, wireline, optical. Networks can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks include local area networks such asEthernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G,LTE and the like, TV wireline or wireless wide area digital networks toinclude cable TV, satellite TV, and terrestrial broadcast TV, vehicularand industrial to include CANBus, and so forth. Certain networkscommonly require external network interface adapters that attached tocertain general purpose data ports or peripheral buses (1649) (such as,for example USB ports of the computer system (1600)); others arecommonly integrated into the core of the computer system (1600) byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). Using any of these networks, computersystem (1600) can communicate with other entities. Such communicationcan be uni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbus to certain CANbusdevices), or bi-directional, for example to other computer systems usinglocal or wide area digital networks. Certain protocols and protocolstacks can be used on each of those networks and network interfaces asdescribed above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1640) of thecomputer system (1600).

The core (1640) can include one or more Central Processing Units (CPU)(1641), Graphics Processing Units (GPU) (1642), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1643), hardware accelerators for certain tasks (1644), graphicsadapters (1650), and so forth. These devices, along with Read-onlymemory (ROM) (1645), Random-access memory (1646), internal mass storagesuch as internal non-user accessible hard drives, SSDs, and the like(1647), may be connected through a system bus (1648). In some computersystems, the system bus (1648) can be accessible in the form of one ormore physical plugs to enable extensions by additional CPUs, GPU, andthe like. The peripheral devices can be attached either directly to thecore's system bus (1648), or through a peripheral bus (1649). In anexample, the screen (1610) can be connected to the graphics adapter(1650). Architectures for a peripheral bus include PCI, USB, and thelike.

CPUs (1641), GPUs (1642), FPGAs (1643), and accelerators (1644) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1645) or RAM (1646). Transitional data can also be stored in RAM(1646), whereas permanent data can be stored for example, in theinternal mass storage (1647). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1641), GPU (1642), massstorage (1647), ROM (1645), RAM (1646), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1600), and specifically the core (1640) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1640) that are of non-transitorynature, such as core-internal mass storage (1647) or ROM (1645). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1640). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1640) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1646) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1644)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

JEM: joint exploration modelVVC: versatile video codingBMS: benchmark set

MV: Motion Vector HEVC: High Efficiency Video Coding SEI: SupplementaryEnhancement Information VUI: Video Usability Information GOPs: Groups ofPictures TUs: Transform Units, PUs: Prediction Units CTUs: Coding TreeUnits CTBs: Coding Tree Blocks PBs: Prediction Blocks HRD: HypotheticalReference Decoder SNR: Signal Noise Ratio CPUs: Central Processing UnitsGPUs: Graphics Processing Units CRT: Cathode Ray Tube LCD:Liquid-Crystal Display OLED: Organic Light-Emitting Diode CD: CompactDisc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random AccessMemory ASIC: Application-Specific Integrated Circuit PLD: ProgrammableLogic Device LAN: Local Area Network

GSM: Global System for Mobile communications

LTE: Long-Term Evolution CANBus: Controller Area Network Bus USB:Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: FieldProgrammable Gate Areas

SSD: solid-state drive

IC: Integrated Circuit CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method of video encoding performed in a videoencoder, the method comprising: determining whether a sequence ofpictures includes a flash picture that is associated with a scene changebetween (i) a first scene of a picture of the sequence of pictures and(ii) a second scene of a prior picture and a subsequent picture of thepicture in the sequence of pictures, the scene change being determinedbased on a content change between the first scene and the second scenebeing larger than a threshold; and performing an encoding process on acurrent picture in the sequence of pictures in response to (i) thepicture being determined as the flash picture and (ii) the picture beingthe current picture.
 2. The method of claim 1, wherein the determiningcomprises one of: determining that the picture is the flash picturebased on a contrast difference between the first scene and the secondscene being larger than the threshold; and determining that the pictureis the flash picture based on a feature difference between the firstscene and the second scene being larger than the threshold.
 3. Themethod of claim 1, wherein: the encoding process includes a temporalfilter process, and the temporal filter process is not performed on thepicture based on the picture being determined as the flash picture andbeing the current picture.
 4. The method of claim 1, wherein: theencoding process includes a temporal filter process, and the picture isexcluded as a reference picture in the temporal filter process based onthe picture being determined as the flash picture and not being thecurrent picture.
 5. The method of claim 4, wherein the performing theencoding process further comprises: in response to the picture beingexcluded as the reference picture in the temporal filter process, addinganother picture to the sequence of pictures as a reference picture forthe temporal filter process such that a total number of referencepictures for the temporal filter process remains constant, the otherpicture and the picture being positioned at a same temporal side of thecurrent picture in the temporal filter process.
 6. The method of claim1, wherein the encoding process includes one of an attribute adjustment,a cost estimation, or a luma mapping with chroma scaling (LMCS) process,the LMCS process including in-loop mapping of a luma component of thecurrent picture and a scaling of a luma-dependent chroma residual of thecurrent picture.
 7. The method of claim 6, wherein: the encoding processincludes the attribute adjustment, and the performing the encodingprocess includes moving the picture to a higher temporal level in thesequence of pictures based on the picture being the flash picture. 8.The method of claim 6, wherein: the encoding process includes theattribute adjustment, and the performing the encoding process includessetting a slice type of the picture as a P slice based on the picturebeing the flash picture.
 9. The method of claim 6, wherein: the encodingprocess includes the attribute adjustment, and the performing theencoding process includes determining the picture as a non-referencepicture of the current picture based on the picture being the flashpicture and not being the current picture.
 10. The method of claim 6,wherein: the encoding process includes the cost estimation, and theperforming the encoding process includes performing the cost estimationto generate a difference between the current picture and a predictionthat is based on a weighted combination of the picture and anotherreference picture of the current picture based on the picture beingdetermined as the flash picture and not being the current picture. 11.The method of claim 1, wherein the performing the encoding processincludes: disabling at least one of bi-direction optical flow (BDOF) ordecoder side motion vector refinement (DMVR) for the current picture inthe encoding process in response to (i) the picture being determined asthe flash picture and being a reference picture of the current picture,and (ii) the current picture being a B type picture with two referencepicture lists.
 12. The method of claim 6, wherein: the encoding processincludes the LMCS process, and the performing the encoding processincludes disabling the LMCS process for the picture based on the picturebeing determined as the flash picture.
 13. The method of claim 6,wherein: the encoding process includes the LMCS process, and theperforming the encoding process further includes: based on the picturebeing determined as the flash picture, determining a set of LMCSparameters for the picture based on an LMCS picture analysis; andperforming the LMCS process on the picture based on the determined setof LMCS parameters.
 14. The method of claim 6, wherein: the encodingprocess includes the LMCS process, and the performing the encodingprocess includes performing the LMCS process on the picture based on apredefined set of LMCS parameters in response to the picture beingdetermined as the flash picture, the predefined set of LMCS parametersbeing generated by training a plurality of general flash pictures. 15.An apparatus, comprising: processing circuitry configured to: determinewhether a sequence of pictures includes a flash picture that isassociated with a scene change between (i) a first scene of a picture ofthe sequence of pictures and (ii) a second scene of a prior picture anda subsequent picture of the picture in the sequence of pictures, thescene change being determined based on a content change between thefirst scene and the second scene being larger than a threshold; andperform an encoding process on a current picture in the sequence ofpictures in response to (i) the picture being determined as the flashpicture and (ii) the picture being the current picture
 16. The apparatusof claim 15, wherein the processing circuitry is configured to performone of: determining that the picture is the flash picture based on acontrast difference between the first scene and the second scene beinglarger than the threshold; and determining that the picture is the flashpicture based on a feature difference between the first scene and thesecond scene being larger than the threshold.
 17. The apparatus of claim15, wherein: the encoding process includes a temporal filter process,and the temporal filter process is not performed on the picture based onthe picture being determined as the flash picture and being the currentpicture.
 18. The apparatus of claim 15, wherein: the encoding processincludes a temporal filter process, and the picture is excluded as areference picture in the temporal filter process based on the picturebeing determined as the flash picture and not being the current picture.19. The apparatus of claim 18, wherein the processing circuitry isconfigured to: in response to the picture being excluded as thereference picture in the temporal filter process, add another picture tothe sequence of pictures as a reference picture for the temporal filterprocess such that a total number of reference pictures for the temporalfilter process remains constant, the other picture and the picture beingpositioned at a same temporal side of the current picture in thetemporal filter process.
 20. The apparatus of claim 15, wherein theencoding process includes one of an attribute adjustment, a costestimation, or a luma mapping with chroma scaling (LMCS) process, theLMCS process including in-loop mapping of a luma component of thecurrent picture and a scaling of a luma-dependent chroma residual of thecurrent picture.